1. Field of the Invention
Embodiments of the present invention generally relate to a method for flexible process condition monitoring.
2. Description of the Related Art
In a process that involves several processing steps, such as a plasma enhanced chemical vapor deposition (PECVD) process whereby RF power is delivered to an electrode in multiple steps at different levels, monitoring the processing conditions may be difficult. Since the process recipe is composed of several sub steps, which each may have different process conditions, process monitoring results show a typical characteristic in each step for each item. However, the allowable deviation ranges are set as an equipment cluster, which is considered as a universal parameter to cover all process conditions. A universal processing condition is not enough to detect a small deviation in a specific step.
As shown in FIG. 1, a process recipe is charted showing six steps. For each of the steps, an acceptable deviation range (an area that defines the acceptable deviation for the RF power level) is defined. The acceptable deviation range for each step is programmed to be substantially identical without any regard to the sensitivity of each step. Thus, while the deviation from the expected value is shown to be within the acceptable deviation range for each step, the deviation from the expected value for the third step may be outside the tolerable limits of the process, yet not detected.
One manner to deal with the problem of FIG. 1 is to simply shrink the acceptable deviation range to the value of the most sensitive process step. In FIG. 1, the third step is the most sensitive process step. Thus, the value of the permissible deviation may be set based upon the third step. In so doing, the process may be overly sensitive and thus, less efficient. The enhanced sensitivity of the process may cause the RF power level to be indicated as outside the acceptable deviation range for a step, even though the indicated RF power level may not have any negative impact upon the process. Such a situation would have a negative impact on substrate throughput.
Therefore, there is a need in the art for a method of flexibly monitoring the conditions of a recipe that has multiple steps with different conditions.